This invention relates to a pressure regulator for restricting hydraulic fluid supplied to a brake system while allowing corresponding substantially unrestricted hydraulic fluid to be supplied to a steering system.
U.S. Pat. Nos. 4,281,585 and 4,362,086 discloses a typical hydraulic brake booster which uses hydraulic fluid generated by a pump in a steering system as a source of power to effect a brake application in response to an operator input. In such brake boosters, a control valve is moved to restrict the flow of fluid from the pump to the steering gear and direct such restricted flow into a control chamber to act on a piston which supplies a master cylinder with a force to effect a brake application. In response to a maximum input force applied by an operator it is possible to nearly interrupt hydraulic flow communication to the steering gear and as a result a power assist in turning the wheels of a vehicle is correspondingly reduced. Further in brake boosters, it is common to have the control chamber connected to an accumulator so that in a situation where the pump is inoperative, a limited amount of pressurized fluid is available to effect a brake application. The accumulator is connected to the hydraulic source and during normal operation of the pump is charged to a same level as the hydraulic fluid supplied to the brake booster. In some vehicles when the engine is operating at a low level of revolution per minute such as when parking, the output of the pump does not offer sufficient power to operate the steering gear in a desired manner. A solution to improve the power assist for the steering gear is to increase the hydraulic pressure available to the steering gear. Unfortunately an increase in fluid pressure in the system may have an adverse effect on the brake booster and components associated with the brake booster such as the accumulator.
A primary object of the present invention is to provide a hydraulic supply system with a regulator which meters the flow of supply hydraulic fluid from a pump supplied to a brake booster to define maximum fluid pressure for assisting in effecting a brake application by directing the flow of supply hydraulic fluid directly to a steering gear once the maximum fluid pressure develops.
In more particular detail, the hydraulic supply system has a regulator with a first housing with a bore therein having a pump inlet connected to receive supply hydraulic fluid, a pump outlet connected to communicated supply hydraulic fluid to an inlet port of the booster, a gear inlet connected to a gear port of the booster, and a gear outlet port connected to the steering gear. The brake booster having a second housing with a control chamber therein connected to a first bore and a second bore. A piston located in the first bore is connected to a master cylinder while a control valve is located in the second bore. The second bore having a supply inlet port for receiving supply hydraulic fluid from the pump outlet of the regulator, the gear port and a return port connected to a reservoir of the pump. Linkage responsive to an input member moves the control valve in the second bore to initially terminate communication between the second bore and reservoir by way of the return port and thereafter moves to restrict the flow of the supply hydraulic fluid presented to supply inlet port by flowing a first portion supply hydraulic fluid to the control chamber while directing the flow of a second portion of the supply hydraulic fluid to the steering gear. The first portion of the supply hydraulic fluid acts on the piston to provide a master cylinder with an operational force to produce a brake application in the wheels of a vehicle. A reserve chamber is connected to the supply inlet port and the control chamber for receiving the supply hydraulic fluid to establish a reserve hydraulic fluid supply. The control valve responds to a desired brake application applied to the linkage by the input member by communicating the reserve hydraulic fluid supply to the control chamber in an absence of supply hydraulic fluid to effect a corresponding brake application. The pump inlet of the regulator receives the supply hydraulic fluid and a spool in bore of the first housing directs the flow of the supply hydraulic fluid through the pump outlet to the inlet port of the housing of the booster. The regulator is responsive to a preset hydraulic fluid pressure that develops in the first portion of the supply hydraulic fluid and is presented to the chamber by metering the flow of the supply hydraulic fluid to the supply inlet port of the brake booster and directly communicating the supply hydraulic fluid to the steering gear. The regulator on metering the flow of the supply hydraulic fluid to the booster supply inlet port establishes a maximum limit for the hydraulic pressure in the first portion of the supply hydraulic fluid as presented to the control chamber and reserve chamber.
An advantage of the hydraulic supply system resides in a regulator which limits the development of the fluid pressure presented to a brake booster and accumulator to a preset value below the capacity of a supply pump.
A further advantage of the hydraulic supply system is provided by a regulator wherein supply fluid delivered by a pump supply fluid to a brake system and steering gear bypasses the brake system when a fluid pressure develops that exceeds a preset value to make a greater quantity of flow available to the steering gear.
A still further advantage of the hydraulic supply system is provided by a regulator which protects a brake booster from a hydraulic fluid pressure above a preset value that is supplied to a steering system from a common pump.